Alaska Bones May Clear Comet as Dinosaur Killer

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Fossils discovered in northern Alaska challenge the widely debated hypothesis that the climatic results of an asteroid or comet's striking the Earth could have killed off the dinosaurs, scientists reported yesterday.

The scientists said they had found strong evidence that the Arctic dinosaurs were not migratory but lived in the region. Although the weather there was milder then, they said, some dinosaur species must have had physiologies enabling them to survive long periods of darkness, very cold temperatures and sparse food supplies. Those conditions are similar to conditions the theoretical asteroid impact would have caused in the period when dinosaurs were becoming extinct.

The analysis of the fossils, collected this summer, was reported in the current issue of the journal Science by a group led by Elisabeth M. Brouwers of the United States Geological Survey and William A. Clemens of the University of California at Berkeley.

The bones, mainly those of duck-billed dinosaurs, or hadrosaurs, were found near the Colville River on the North Slope of Alaska. The site was perhaps 350 to 1,000 miles farther north at the time these dinosaurs lived, 76 million to 66 million years ago. Clues in Other Bones

The primary clue that they were not migratory, scientists concluded, was the presence of many bones of young animals. Dr. Clemens, a paleontologist, said in a telephone interview that it was unlikely that young could have kept up with an adult group migrating many hundreds of miles from a southern region.

''If the North Slope dinosaurs were not migratory,'' the scientists wrote, their occurrence at high northern latitudes ''provides direct evidence of the ability of some species to tolerate up to several months of darkness and to cope with cold air temperatures. Thus, some of the proposed effects of impacts of an asteroid or comets, increased volcanism, or related hypotheses may not have been the direct cause of the demise of the dinosaurs.''

An examination of pollen and plant fossils in the same sediments showed that the environment was relatively mild, although frosts probably occurred in the Arctic's winter darkness. The area was a river delta with a predominance of deciduous forests.

The absence of plentiful evergreen vegetation, the scientists said, ''would result in an annual period of stress for herbivorous hadrosaurids, during which they had to cope with a greatly reduced food supply.'' They said the dinosaurs might have survived the chill dark through a kind of semi-hibernation. 'Prospecting' for More Proof

Dr. Clemens said further explorations near the Colville River would emphasize ''general prospecting'' for fossils of animals that were the dinosaurs' contemporaries. Finding remains of turtles or crocodiles or other reptiles of the period would help establish that the dinosaurs were not migratory, he said. Such remains are usually found in permanent dinosaur habitats.

The theory that a large object crashed into the Earth to destroy the dinosaurs was advanced in 1979 by Luis W. Alvarez, a Nobel Prize-winning physicist, and his son Walter, a geologist. Both are affiliated with the University of California at Berkeley.

Support for the theory is strong among geologists who keep finding possibly extraterrestrial chemical clues in 65-million-year-old sediments around the world. But paleontologists, while agreeing that the impact may have occurred, have been skeptical about linking the disaster and the dinosaur extinctions.

A version of this article appears in print on , Section A, Page 19 of the National edition with the headline: Alaska Bones May Clear Comet as Dinosaur Killer. Order Reprints | Today’s Paper | Subscribe